Serum lactate is an important biomarker for hypoperfusion and is useful in patient monitoring from critical care medicine to perioperative management. Serum lactate has, for instance, been shown to be an independent predictor of mortality in sepsis patients and an independent predictor of major complications after cardiac surgery; it is capable of stratifying patients by risk for developing shock; and serum lactate level also serves as a useful target for quantitative resuscitation. Current methods and systems for estimating serum lactate require a blood draw and laboratory test, which incur cost and delay.